Background: Chronic placental inflammation, such as villitis of unknown etiology (VUE) and chronic chorioamnionitis (CCA), is considered a placental manifestation of maternal anti-fetal rejection. The aim of this study is to investigate its frequency in twin pregnancies compared to singleton pregnancies.

Methods: Three hundred twin placentas and 1,270 singleton placentas were consecutively collected at a tertiary medical center in Seoul, Republic of Korea from 2009 to 2012. Hematoxylin and eosin sections of tissue samples (full-thickness placental disc and chorioamniotic membranes) were reviewed.

Results: Non-basal VUE was more frequent in twin placentas than in singleton placentas (6.0% vs 3.2%, p < .05). In preterm birth, CCA was found less frequently in twin placentas than in singleton placentas (9.6% vs 14.8%, p < .05), reaching its peak at an earlier gestational age in twin placentas (29-32 weeks) than in singleton placentas (33-36 weeks). CCA was more frequent in twin pregnancies with babies of a different sex than with those with the same sex (13.8% vs 6.9%, p=.052). Separate dichorionic diamniotic twin placentas were affected by chronic deciduitis more frequently than singleton placentas (16.9% vs 9.7%, p

Conclusions: The higher frequency of non-basal VUE in twin placentas and of CCA in twin placentas with different fetal sex supports the hypothesis that the underlying pathophysiological mechanism is maternal anti-fetal rejection related to increased fetal antigens in twin pregnancies. The peak of CCA at an earlier gestational age in twin placentas than in singleton placentas suggests that CCA is influenced by placental maturation.

f2-jptm-2015-09-09: The frequency of villitis of unknown etiology (VUE) in twin placentas according to the gestational age. (A) VUE in singleton and twin placentas is found more frequently as gestational age at birth increases. (B) Non-basal VUE is more frequent in twin placentas than in singleton placentas at term (**p<.01). (C) There is no significant difference in the frequency of basal VUE between singleton and twin placentas. GAD, gestational age at delivery

Mentions:
The frequency of VUE increased with increasing gestational age at birth in both singleton and twin placentas; however, there was no significant difference in the frequency of VUE between singleton and twin placentas when the cases were matched by gestational age (Fig. 2A). When the study population was divided into preterm and term births, term twin placentas were affected by non-basal VUE more frequently than term singleton placentas (12.9% [9/70] vs 3.6% [14/384], p<.01), but the difference was not detected in preterm placentas (Fig. 2B). The frequencies of basal VUE were not significantly different between singleton and twin placentas either at preterm or at term (Fig. 2C).

f2-jptm-2015-09-09: The frequency of villitis of unknown etiology (VUE) in twin placentas according to the gestational age. (A) VUE in singleton and twin placentas is found more frequently as gestational age at birth increases. (B) Non-basal VUE is more frequent in twin placentas than in singleton placentas at term (**p<.01). (C) There is no significant difference in the frequency of basal VUE between singleton and twin placentas. GAD, gestational age at delivery

Mentions:
The frequency of VUE increased with increasing gestational age at birth in both singleton and twin placentas; however, there was no significant difference in the frequency of VUE between singleton and twin placentas when the cases were matched by gestational age (Fig. 2A). When the study population was divided into preterm and term births, term twin placentas were affected by non-basal VUE more frequently than term singleton placentas (12.9% [9/70] vs 3.6% [14/384], p<.01), but the difference was not detected in preterm placentas (Fig. 2B). The frequencies of basal VUE were not significantly different between singleton and twin placentas either at preterm or at term (Fig. 2C).

Background: Chronic placental inflammation, such as villitis of unknown etiology (VUE) and chronic chorioamnionitis (CCA), is considered a placental manifestation of maternal anti-fetal rejection. The aim of this study is to investigate its frequency in twin pregnancies compared to singleton pregnancies.

Methods: Three hundred twin placentas and 1,270 singleton placentas were consecutively collected at a tertiary medical center in Seoul, Republic of Korea from 2009 to 2012. Hematoxylin and eosin sections of tissue samples (full-thickness placental disc and chorioamniotic membranes) were reviewed.

Results: Non-basal VUE was more frequent in twin placentas than in singleton placentas (6.0% vs 3.2%, p < .05). In preterm birth, CCA was found less frequently in twin placentas than in singleton placentas (9.6% vs 14.8%, p < .05), reaching its peak at an earlier gestational age in twin placentas (29-32 weeks) than in singleton placentas (33-36 weeks). CCA was more frequent in twin pregnancies with babies of a different sex than with those with the same sex (13.8% vs 6.9%, p=.052). Separate dichorionic diamniotic twin placentas were affected by chronic deciduitis more frequently than singleton placentas (16.9% vs 9.7%, p

Conclusions: The higher frequency of non-basal VUE in twin placentas and of CCA in twin placentas with different fetal sex supports the hypothesis that the underlying pathophysiological mechanism is maternal anti-fetal rejection related to increased fetal antigens in twin pregnancies. The peak of CCA at an earlier gestational age in twin placentas than in singleton placentas suggests that CCA is influenced by placental maturation.